The cornea is made of a series of layers. In humans, the anterior layer, known as the epithelium, serves the function of maintaining the integrity of the cornea. Components of epithelial cells regulate the transport of fluids and electrolytes through lamellae of the stroma, which is separated from the epithelium by a thin layer known as the Bowman's membrane. Beneath the stroma is another layer, Descemet's membrane, which separates the stroma from the endothelium, a thin layer of cells forming the posterior surface of the cornea.
Between the endothelial layer of the cornea and the lens of the eye is the anterior chamber. The anterior chamber contains fluid, known as the aqueous humor, which is produced by the eye.
The cornea and lens of the eye can be subject to trauma as a result of disease, injury to, or surgery on the eye. Given the delicate nature of the eye, it is important to have the rate of healing from such traumas be as rapid as possible and to minimize undesirable effects associated with natural wound-healing processes, such as scarring and contraction of healed tissues. Such effects can interfere with visual function.
One of the dangers of any trauma to the eye is damage to the endothelium. Endothelial cells in adults mitose only rarely, and the population of endothelial cells generally decreases with age; thus, it is important that damage to these cells be minimized and healing be enhanced.
There have been a number of advances in ophthalmic surgery in recent years which have provided great benefits but which also have increased the risk of damage to or destruction of endothelial cells during the surgical procedures. For example, intraocular lens (IOL) implantation and corneal transplantation can result in damage to endothelial cells. The risk to the cells can be great, for simply having the cells come into contact with, for example, surgical instruments, can result in what is known as a "touch injury."
A number of efforts have been made to find ways to protect endothelial cells during or following surgical procedures. For example, U.S. Pat. No. 4,713,446, issued to DeVore et al. (1987), describes injecting viscoelastic collagen solutions into the anterior chamber of the eye to maintain anterior chamber depth during surgery. If the depth of the chamber cannot be maintained, the cornea can collapse toward the lens, increasing the risk that the endothelium will suffer a touch injury. The viscoelastic materials help to protect cell surfaces from mechanical trauma and create space by keeping adjacent but not adherent tissue surfaces separated during surgical procedures. The use of other viscoelastic compositions also have been described. See, for example, Pape, L. G. et al., Am. Acad. Ophthal., 87(7):699 (1980), which describes the use of viscoelastic compositions of hyaluronic acid in a variety of anterior segment surgical procedures.
Although the viscoelastic compositions described in these and other references have proven to be useful, further methods are desired to help protect endothelial cells and enhance wound healing.